Although the enhancement of the primordial scalar spectrum only leads to light, evaporating PBHs, it will act as an efficient second order source for the primordial tensors [1]}, [2]}, [3]}, [4]}, [5]}. To compute the power spectrum of the GW energy density today we follow the semi-analytical approach given in Ref. [4]}. The energy density parameter for GW per logarithmic \(k\)  interval today is given by:
\(\Omega _{GW,\,0} = \frac{\rho _{GW} (k)}{\rho _{T,\,0}} = 0.39 \left( \frac{g_* (T_c)}{106.75} \right)^{-1/3} \Omega _{r,\,0} \Omega _{GW}(k, \tau _c) \,,\) 
